Archive for June, 2015

It began as a persistent high pressure weather pattern over the Gulf of Alaska in the autumn of 2013. With more sunshine and lighter winds, it prevented the usual extent of winter cooling of the sea surface, and so it caused an offshore region of warmer than usual water to form.

And then it expanded into something huge, got named The Blob, and sea surface temperatures rose more than 3 degrees C (5 degrees F) warmer than average, warmer than anything on record. During 2014-2015 it moved shoreward bringing warm weather to the West coast from Alaska south to the North West States, reducing the snow pack and all that implies.

The Pacific Blob has expanded into three major parts extending south along the west coast of North America. The darker the red, the warmer the sea surface temperature relative to recent averages (noaa.gov)

It also has also created relative havoc in the coastal waters: the southerly flowing cool coastal California Current has weakened, warmer water has pushed north, and sub-tropical species of fish are turning up in the Gulf of Alaska.

This past month a most astonishing crab, the Red Tuna Crab, Pleuroncodes planipes, has also turned up, stranding by the thousands upon thousands on the shores of Southern California from Ocean Beach to La Jolla. This is a crab that looks as if it wants to be a shrimp. It spends its whole life cycle swimming in the water column off the bottom, voraciously eating plankton, forming immense swarms, fed on by whales, porpoises, larger fish and seabirds Not by humans though, because of some toxins it carries.

The Red Tuna Crab Pleuroncodes planipes swims up and down in the water column, its uncurled tail making it look more like a shrimp, but it is still a crab (scripps.ucsd.edu)

Vast swarms of the Red Tuna Crab have stranded this past month on beaches in Southern California (usatoday.com)

Normally it lives in the warmer water of the Gulf of California and along the west coast of Baja. Subject to winds, tides and currents, in warmer years – El Nino years, for instance – stranded swarms are not that unusual on the shores of southern California. But of course, the past couple of years have not been El Nino years.

They have been the years of The Pacific Blob.

We don’t know yet the full extent of the impact of The Blob. But fish that have been seen far north of their regular sub-tropical coastal waters, even to the Gulf of Alaska, include skipjack tuna and albacore, Ocean Sunfish and Thresher Sharks. The strandings of the siphonophore jellyfish Velella in the summer of 2014, the starving Cassin’s Auklets, the starving California Sea Lion pups now dying along many parts of the west coast – these are all probably victims of The Blob.

Among many associated problems, fewer nutrients are reaching the warmer surface waters, chlorophyll amounts have dropped – affecting plankton abundance – and a lack of small fish for foraging adult auklets and sea lions may explain their starving and dying offspring.

How will the salmon of the Alaskan, BC and Northwest coasts be affected? Well, we’ll see soon enough, but it cannot be good.

Why did this all happen? There is an intriguing link to weather patterns in the southern tropical Pacific, but nothing certain. Is there a link to climate change? We don’t know. How will it end? It just needs the winds of the Gulf of Alaska to pick up again, and all should return to normal.

The elusive normal. What we know is that most marine animals are closely tied to the sea temperatures around them. We know that now, finally, after several years of inaction, a new and seemingly major El Nino is developing, the first like this since the crippling one of 1997-19978, and the warm coastal temperatures will persist.

At the least we are probably getting a preview of what warming oceans will be like on the west coast in the decades ahead. Not reassuring perhaps, but fascinating none the less.

The swiftest and largest predatory fish – tuna, some sharks, billfish like marlins – warm their swimming muscles a few degrees warmer than the surrounding water, and thereby get the extra speed they need to race down prey. Though the rest of their bodies are mostly unwarmed, the same temperature as the water around them, it is a remarkable adaptation.

Tbey do this through a complex heat-exchange tangle of arteries and veins (rete mirabile) near their swimming muscles, conserving the heat instead of losing it all when when the blood flows through the gills where it is cooled to the ocean ambient temperature while it is re-oxygenated. These fish usually also tend to stay near the surface, where it is warmer, dropping down into deeper colder water only to hunt.

Now we know that at least one species, the Opah Lampris guttatus, is endothermic. Not as hot as as mammals and birds are, but surprisingly warmer than the water around them. In 10 degree C water, in a 40 kg fish, muscles and internal organs are about 5 degrees warmer, and the brain and eye muscles a couple of degrees even warmer than that.

Opah also avoid surface waters: they are mesopelagic, living circumglabally at depths 50 to 400 m below the surface. And they are predators, apparently of squid, though they lack the streamlined form we expect of predatory fish.

On the left, internal temperatures, 5 cm below the skin, of a 40 kg Opah in 10.5 degree C water. On the right, temperature of pectoral muscles of a free swimming Opah (red) at depths of 70 meters or more (temp blue, depth black) (science.org)

How do they stay so warm? Their heat is generated by their pectoral muscles, and they too have rete mirabile heat-exchange system, but unlike all other fish, theirs are in their gills, the harshest place they could be. To help conserve their body heat, their skin is unusually thick, and under their skin they have an unusual layer of insulating fat.

The warmer muscles, brain, sense organs and heart all give Opah the advantages of a warm blooded predator in a cold blooded world – more alert, faster. Its body shape is puzzling though – what kind of predatory fish has a body shaped like a disc? Perhaps we don’t know enough about this yet.

What’s ahead for this species in a world where we eat as many fish as we can catch? Though it lives where it is relatively safe from us, it not uncommon as bycatch on the hooks of longline fishers. It also is turning up now in fish markets, and apparently makes for good sushi.

Circumglobal range of Opah (also known as Moonfish). Red denotes regions where it most common. *chefs-resources.com)

But it doesn’t form vulnerable schools, it keeps away from surface waters, its range is very large, and as long as its own food supplies persist, it isn’t severely threatened. Or so it seems, anyway.

It would be nice to understand it better but otherwise, really, let’s just leave it alone, and hope it makes it through these challenging times.